The present invention relates to a three-dimensional graphene composite, a preparation method for the same, and a supercapacitor comprising the same, and more particularly to a three-dimensional graphene composite including at least one electrode material nanoparticle selected from a transition metal hydroxide, a transition metal oxide and a conducting polymer as adsorbed onto the surface of a three-dimensional graphene foam, a preparation method for the three-dimensional graphene composite, and a supercapacitor including the three-dimensional graphene composite.
With a recent rapid increase in the demands for portable electronic devices, energy storage devices capable of supplying high energy and high electric power are in great demand. In response to this, supercapacitors with relatively high energy density and high power density are highly favored as one of the electrochemical capacitors that have intermediate characteristics between electrolytic condensers and secondary batteries.
Supercapacitors, also called ultracapacitors, refer to an energy storage unit noticeably far higher in capacity than the conventional condensers or electrolytic capacitors. Supercapacitors are used as a power source that is able to hold a large amount of energy and emit high energy for several scores of seconds to several minutes. Supercapacitors are under spotlight in various industrial fields such as energy storage units for hybrid car, memory backup units for electronic device, industrial power supply, etc., as they are suitable to fill in the regions of performance characteristics in which the conventional energy storage units such as condensers (offering high power density but low energy density) or secondary batteries (offering high energy density but low power density) leave much to be desired.
There are three types of supercapacitors: electric double layer capacitors (EDLCs), pseudocapacitors, and hybrid capacitors.
EDLCs, utilizing physical adsorption/desorption of ions onto the surface of activated carbon to store the energy, advantageously exhibit high power characteristics, high charge/discharge efficiency and semi-permanent charge/discharge cycle but cannot meet the demands for high power because of their low specific capacity (SC), which is merely about one tenth of the specific capacity of lithium secondary batteries.
Hybrid capacitors, which use an active material applying a different mechanism to cathode and anode electrodes, offer higher energy density than the other types of capacitors but still has the difficulty of commercialization due to extreme complexity in the design and fabrication of the plate elements and high production cost.
Pseudocapacitors use the oxidation-reduction reaction of an active material of metal oxide or polymer with protons (Hf) in an aqueous electrolyte and have the limit of the working voltage to a certain value or below. But, there is a growing interest in the pseudocapacitors, which have the high energy density, several times higher than that of the EDLCs.
In general, examples of the materials for pseudocapacitor include metal oxides, metal hydroxides, or conducting polymers, which are very susceptible to the oxidation-reduction reaction. These materials are characterized by having a plurality of oxidized forms/structures. RuO2 is emerging as one of the promising materials for pseudocapacitor but highly expensive and rate, so its application is much limited. Accordingly, there is a demand for developing a material for capacitor electrode that offers high specific capacity (SC) based on low cost and sufficient resource.